Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$97.98	3.255%	$101.1692	$101.17	$101.15	$101.20
Purchase #2	$153.76	13.125%	$173.941	$173.94	$173.95	$173.90
Purchase #3	$35.98	6.121%	$38.1823	$38.18	$38.20	$38.20
Purchase #4	$46.31	12.706%	$52.1941	$52.19	$52.20	$52.20
Purchase #5	$132.96	8.196%	$143.8574	$143.86	$143.85	$143.90
Purchase #6	$145.85	7.121%	$156.236	$156.24	$156.25	$156.20
Purchase #7	$152.32	11.153%	$169.3082	$169.31	$169.30	$169.30
7 purchase totals =	$765.16		$834.8882	$834.89	$834.90	$834.90